By Richard N. Waldman, MD
President, The American Congress of Obstetricians and Gynecologists
The due date is one of the most important dates on an expectant mother’s calendar. It gives women an idea of when their babies will come and a timeline to prepare for the arrival. But as many mothers can tell you, the due date is an estimate, not a definite, and can be hard to predict.
Doctors calculate your due date by determining the first day of your last menstrual period and adding 280 days (40 weeks)—the length of an average pregnancy—to that date. The due date is usually set early on in pregnancy and an ultrasound exam may be used to help confirm the gestational age of the fetus. However, only five percent of babies are born on their due date, with many women giving birth as much as three weeks before or two weeks later.
If a woman has not delivered at or after the 42nd week, the pregnancy is considered post-term. Roughly 10% of pregnancies are post-term, which can up the chance of health problems for the woman and her fetus. The placenta may not function as well as it did earlier in the pregnancy, the umbilical cord may become pinched, and the amount of amniotic fluid in the amniotic sac may begin to decrease. The risk of cesarean delivery also doubles in women who are beyond their due date. Despite these risks, most babies born late are healthy.
So what can you expect after your due date passes? After 41–42 weeks of pregnancy, your doctor may perform tests to monitor the fetus’s health—such as fetal heart rate testing, ultrasound evaluation of amniotic fluid volume, or a biophysical profile—several times each week. You may also be instructed to count and record the number of kicks your baby makes in a given amount of time or at certain times during the day. Your doctor may use medications that contain prostaglandins or devices or substances designed to quicken cervical ripening—a softening, thinning, and opening of the cervix— that gets the body ready for labor.
If you don’t start labor on your own by 41–42 weeks, several common techniques may be used to induce it. Your doctor can sweep a gloved finger over the thin membrane that connects the amniotic sac to the uterus (“stripping the membrane”), or may break your water by making a hole in your amniotic sac. You may be given misoprostol or oxytocin to stimulate or intensify contractions. In some instances, cesarean delivery may be necessary if a woman’s labor still does not progress.
For more information, the Patient Education Pamphlet “What to Expect After Your Due Date” is available at www.acog.org/publications/patient_education. ?
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